1. Field of the Invention
The invention relates to the technical elements of prostheses mainly used in orthopedic surgery, particularly those known under the name of lengthening nails for long bone or similar.
We know that following malformations or congenital deficiencies or following fractures, loss of bone substance, or other, some bones such as humerus, femur, tibia, etc. are too short, creating an asymmetry or hypometry.
In the case of lower limbs, for a small discrepancy, below 3 cm, we can use insoles or orthopaedic shoes.
2. Description of Related Art Including Information Disclosed Under 37 CFR §§1.97 and 1.98
For a larger discrepancy or shortening, we can use, for a lengthening of the shorter limb, surgical solutions involving currently two methods, based respectively on external fixators or internal fixators.
In the technique based on external fixators, we use an external apparatus with some parts of it (e.g. metal wires) transfixing soft tissues to reach the bone to which they are secured. The apparatus is accessible from outside the limb, and the advantage of this technique is to allow the Practitioner to act on the apparatus at specified periods of time to induce in a gradual way some lengthening of the bone, generally at its diaphyseal level, after its section. However, these external fixators present mainly the following limitations: they are bulky and unsightly, patients in whom they are implanted sometimes cope with them with difficulty, and they result in significant risk of infection.
The technique based on internal fixators operates in a full internal way, i.e. no part is outside the limb. For this, we generally use nails called intramedullary nails or osteosynthesis plates properly fixed to the bone. The advantage of this solution with respect to the previous one lies in the fact that no device appears outside the limb. However, it is possible to obtain lengthening of the bone only through repeated surgical procedures, allowing, for each one, to obtain a fixed gain, limited by the elastic and plastic yield stresses on the soft tissues at stretching. In addition, in case of large non-gradual lengthening, the filling of the dimensional gap is inconstant and requires adjuvant means to the osteosynthesis, for instance bone grafts, which decrease the mechanical and physiological properties of the lengthened bone.
Technique of the Intramedullary Lengthening Nail
To overcome these drawbacks, the Applicant has made an original elongation nail (CAI), which was protected by patents, including EP 0,346,247. This achievement has as its goal to create a lengthening system combining the advantages of external fixators for a fully adjustable gradual lengthening, and benefits of internal fixators, without the drawbacks of both lengthening systems.
Other intramedullary lengthening nails have been made.
For example, there is one that operates with rotations performed through maneuvers, which cannot be controlled with full security. The patient may over-lengthen in a very short time, which can lead to neurological complications or non-solidification of the bone.
Other intramedullary nails exist, like the one described in EP-A-1477123, which does not operate through rotation, but with two tubes which separate from one another translationally thanks to a part fixed into the pelvis, thus preventing hip motion.
Another, called ‘electronic nail’, is described in U.S. Pat. No. 6,245,075. It features an electric drive, which leads to security problems. Lack of charging during elongation has limited its clinical value.
We can also mention the intramedullary lengthening nail described in U.S. Pat. No. 5,704,939.
These lengthening systems according to the prior art have not diminished the qualities of the original elongation nail (CAI) mentioned above or its clinical interest, because they have some flaws, including lack of full weight bearing during the lengthening and operation with random failures.
Principle of Operation of the Initial Elongation Nail (CAI)
The original lengthening nail (CAI) according to the document mentioned above is remarkable as it is configured to fix at least two parts of the same bone, sectioned into two parts, and it is made of parts able to confer a gradual lengthening, resulting from a partial rotation applied by external maneuvers on the limb concerned, and/or acquired automatically during physiological motion of the limb, for instance while walking, and it is also made of parts for maintaining the obtained lengthening after each rotation applied on the limb and the neutral rotation of bone segments of the limb concerned.
This nail mainly comprises a sleeve within which is mounted, with translational displacement capacity, a tube with suitable means adapted to cause relative displacement of the sleeve and the tube as a result of rotational movements applied to the limb in one direction corresponding to a lengthening of the bone, and in the other direction of rotation to achieve the blocking of the translation of the tube with respect to the sleeve. Translation is obtained by means of ratchet teeth.